1. Field of the Invention
The present invention relates to a fuse, and in particular, to a time lag fuse designed to withstand certain peak inrush currents.
2. Discussion of Related Art
Time lag or time delay fuses are well known in the art. See, for example, U.S. Pat. Nos. 4,517,544; 4,189,696; 4,189,696; 4,680,567; 4,445,106; and 4,409,729. Such fuses are frequently in the form of spiral wound fuses. In a spiral wound fuse, the fuse element is spirally wound around a core that is internal to the fuse body.
However, most prior art spiral wound fuses were at least 5 mm in diameter and 15 mm long, with a voltage rating of only 250 volts. In fact, most spiral wound prior art fuses are 6 mm in diameter and about 32 mm long.
However, certain applications require fuses having a diameter of 3 mm and a length of about 10 mm. Furthermore, the Underwriters Laboratories recently changed the standards for endurance testing of certain fuses. See .sctn.28.2 of UL Standard 497A. The new standard requires certain fuses to have endurance conditioning such that they can withstand a 14 amp pulse having 10/1000 microsecond wave form. Under this standard, the fuse must be able to withstand 100 pulses that reaches 14 peak amps within 10 microseconds and will decay to half-value in 1000 microseconds. Fifty of these pulses are to be at one polarity, and then the pulses are to be repeated at the opposite polarity.
Prior to the present invention, no 3.times.10 mm fuses were able to be made which would comply with the standard and which would have a 350 mA continuous ampere rating and 600 volts DC rating.